This invention relates to processes for monitoring the exhaust gas conversion rate of an exhaust catalyst for an internal combustion engine.
German Patent No. 41 00 397 discloses a process for monitoring the exhaust gas conversion rate of a catalyst for an internal combustion engine in which temperature values are determined at at least two points in the exhaust line during operation of the engine and compared in a control unit to obtain a monitoring signal. The process disclosed in this patent is based on the so-called disturbance-variable principle in which an abnormal operating condition is deliberately produced in a specific operating mode of the internal combustion engine. In the described process the abnormal operating condition is an overrun phase of the internal combustion engine produced by the generation of misfires and by the supply of a defined fuel/air mixture to produce a reaction at the catalyst. To obtain a monitoring signal, the chemical reaction of the catalyst to this mixture is evaluated from the temperature values recorded in the exhaust line.